What does the annotation do? [ConfigurationElementType(typeof(CustomCacheManagerData))]
Would I have to configure something in the web.config for this to work?

Also in the web.config what should this be changed to, to pick up the custom cache manager?
<cacheManagers>
<add name="CurrentCacheManager" type="Microsoft.Practices.EnterpriseLibrary.Caching.CacheManager, Microsoft.Practices.EnterpriseLibrary.Caching, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" expirationPollFrequencyInSeconds="36000"
maximumElementsInCacheBeforeScavenging="3000" numberToRemoveWhenScavenging="10" backingStoreName="inMemory"/>
</cacheManagers>